The present invention relates to a process for separating sulphuric acid and nitric acid from dintrotoluene mixtures.
A generally employed process for the production of dinitrotoluene involves nitrating toluene in a first stage with nitric acid in the presence of sulphuric acid (mixed acid), separating the mononitrotoluenes obtained from the reaction mixture and then further nitrating them with mixed acid in a second stage to form dinitrotoluenes (See for example Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Vol. 13, p 844 et seq). The crude dinitrotoluene mixture obtained after separation of the mixed acid contains further fractions of dissolved or finely dispersed nitric acid and sulphuric acid. In the known processes, this crude dinitrotoluene mixture is washed with water in a suitable apparatus, optionally with addition of bases, and the acid residues pass into the washing water and therefore into the waste water.